The masses of \(Z_b\)  and \(Z_b^\prime \)  are close to the thresholds of \(B^\ast {B}\)  and \(B^\ast \bar{B}^\ast \) , respectively. Following the formulas in Ref. [1]}, [2]}, the velocities of bottom mesons involved in the meson loops can be evaluated as,
\(v=\frac{v_1+v_2}{2}=0.15\sim 0.16,\) 
